Portable radiotelephones having a flip cover are well-known devices offered by several manufacturers. The flip element is a hinged cover which extends over an integral keypad or a portion of the keypad. One example of a hinged cover extending over the whole of the keypad is presented in U.S. Pat. No. 4,845,772. The flip cover may contain a microphone as described in U.S. Pat. No. 4,897,873 or an integral antenna as presented in U.S. Pat. No. 5,170,173. When closed, the flip element provides protection to the keypad from unintentional activation or exposure to the elements. When opened, the flip element provides a convenient extension to the phone and, when fitted with a microphone, is well-positioned to receive audio input from the user's mouth. In addition to these tangible benefits, there is also an unqualified consumer appeal for such flip elements.
FIGS. 1 to 4 show a conventional radiotelephone 100 with front 110 and rear 120 faces, and a flip cover 160 shown in closed (FIGS. 1 and 2) and open (FIGS. 3 and 4) positions. A display 150, speaker 140, microphone 170, and keypad 180 are disposed on the front 110 of the radiotelephone. In this example, the microphone 170 is located not in the flip cover 160 but within the main body of the radiotelephone. With this arrangement, the flip cover opens as is shown in FIGS. 3 and 4. When open, the flip cover directs sound pressure into the microphone 170. When the flip cover 160 is closed, sound pressure passes through an aperture 190 in the cover positioned over the microphone 170. The angle .theta. between the open cover and the front face of the radiotelephone is specified to be 158 degrees by the CCITT Specification. Such an arrangement is well-known to those skilled in the art.
As the technology regarding radiotelephones matures, it is expected that these devices will enjoy further miniaturization. Indeed, in less than a decade radiotelephones have progressed from bulky vehicular mounted devices to compact hand held appliances which can easily fit into a shirt pocket. This trend towards miniaturization however presents several drawbacks.
Consider, for example, that the necessity for human interface imposes certain minimum requirements. For example, it is obvious that as a two-way communication device, a portable radiotelephone must include both a microphone and a speaker. In addition, a radiotelephone must have disposed somewhere on its outer surface a display for providing visual information and a keypad for accepting user inputs. Indeed, to provide even minimal functionality, the keypad must also have a certain number of keys (e.g., 0 through 9 inclusive, a "#" key and a "*" key). Human interface devices must, of course, also meet certain minimum physical requirements which, if exceeded, would make the radiotelephone inconvenient to operate. For example, the keys on the keypad must be of a size which is commensurate with the operator's fingers. The display must also be large enough such that even a user with moderate visual acuity can easily read the characters. Further, the speaker should be optimally located over the user's ear and the microphone positioned directly in front of the user's mouth.
As the overall dimensions of the radiotelephone shrink, so does the space available for the interface devices. Although the radiotelephone itself may become smaller, for example, the average distance between a user's ear and mouth is not expected to change much. Therefore, some consideration must be given to the challenge of packaging, on a rapidly shrinking radiotelephone, devices which must accommodate more static requirements.
The keypad and the display are generally disposed on the same surface of the radiotelephone. Similarly, the speaker and the microphone are also generally on the same side of the radiotelephone. If the speaker and microphone are positioned on the opposite side of the radiotelephone from the display and keypad, then a difficulty arises as to the positioning of the flip cover. The flip cover should cover the keypad when closed and, when opened, assist in the operation of the microphone.
Consider, for example, that for optimum sound quality the speaker should be positioned directly over the ear and the microphone positioned directly in front of the operator's mouth. Such an arrangement mandates a certain minimum separation between the speaker and microphone, e.g. 6 inches. Consider that with a miniaturized radiotelephone the microphone will likely be positioned over the operator's cheek, away from the mouth. This results in a loss of sound pressure level (SPL) at the input to the microphone. Tests have shown sound pressure levels reaching the microphone adjacent the cheek to be more than 10 dB lower compared to the ideal location when the microphone is in front of the mouth. Although the reduction of SPL can be compensated for by increasing the gain of the audio amplifiers to which the microphone signal is coupled, the signal to noise ratio cannot be corrected. Consequently, when a radiotelephone with a microphone adjacent the cheek is used in the presence of ambient noise the sound quality of the communication will suffer.
A flip cover element has the desirable quality that it extends the overall dimensions of the radiotelephone. In this regard, mounting the microphone in the flip cover may serve to position the microphone in a more advantageous position, such as closer to the user's mouth. Indeed, a well-designed flip element will also direct sound pressure from the user's mouth towards a microphone embedded within a surface of the main body of the radiotelephone. However, if the flip element is also intended to cover the keypad when closed it is not obvious how to also accommodate the requirements of a microphone mounted on the reverse side opposite to the keypad.
It is an object of the present invention to provide a miniaturized radiotelephone capable of incorporating many of the interface features commonly found on present radiotelephones. It is a further object of the present invention to provide a flip cover element capable of substantially covering the keypad of a miniaturized radiotelephone when closed and offering an advantageous position for the placement of a microphone when open.